A physiological and biochemical approach to selecting the ideal diet for Ostrea edulis (L.) broodstock conditioning (part A)

Abstract

To select the best microalgae for Ostrea edulis conditioning, four single species diets were fed to batches of broodstock, which were then compared using physiological and biochemical approaches. Ingestion and absorption were first studied, showing that Chaetoceros gracilis and Skeletonema marinoï were efficiently ingested (4.9–5.3 mg g−1 h−1) and absorbed (1.9–2.5 mg g−1 h−1) while Tetraselmis suecica led to the lowest physiological responses (0.36 and 0.12 mg g−1 h−1 respectively). When O. edulis were fed any microalgae except T‐ISO with only 79 mg g−1, gonads accumulated carbohydrates from 116 to 141 mg g−1 and the extent of accumulation depended on the species supplied in the order T. suecica<C. gracilis<S. marinoï. When oysters were fed either of the diatoms (C. gracilis or S. marinoï), an efficient transfer of 20:5(n‐3) to all tissues, including the gonads, was recorded while no enrichment in 22:6(n‐3) occurred in all tissues (polar fraction) when oysters were fed T‐ISO. In contrast (22:5(n‐6)), a characteristic fatty acid of T‐ISO accumulated in all tissues, confirming its allocation despite particularly low ingestion (1.66 mg g−1 h−1) and absorption (0.32 mg g−1 h−1). When oysters were fed C. gracilis or S. marinoï an efficient transfer of cholesterol and campesterol from diatoms to the gonads was observed, while no sterol accumulation occurred in the gonad when fed T. suecica. Because of low ingestion, absorption and poor biochemical compounds' transfer, T. suecica is not recommended for O. edulis conditioning. T‐ISO also exhibited low physiological performances but due to a specific 22:6(n‐3) enrichment in the gonad neutral fraction (16.1%), its potential role in reproduction should be considered. Chaetoceros gracilis is highly recommended for O. edulis broodstock while a source of DHA other than that provided by T‐ISO should be found due to its poor absorption. Because a mixed diet has been shown to be more efficient for O. edulis broodstock conditioning, complementary trials dealing with the effects of other species rich in 22:6(n‐3) such as Rhodomonas salina or Pavlova lutheri should be performed.

The selection of an ideal diet for Ostrea edulis (L.) broodstock conditioning (part B)

“…The results of the present study differ in that the fatty acid profiles of main tissues did not show a clear correlation with the diets as it has been shown in our previous work with four other microalgae ( Fig. 3; González-Araya et al, 2010). These results were unexpected, because fatty acid composition in microalgae is generally specific.…”

“…(51%). Although the oysters fed R. salina showed the best ingestion and absorption of the study, the values remained lower than those previously reported with C. gracilis and S. marinoï (≈ 5 mg g −1 h −1 : González-Araya et al, 2010). Absorption efficiency (ae%) ranged from 33 to 51%, while those obtained with the four other microalgae tested in our sister study ranged from 19 to 46% (González-Araya et al, 2010).…”

“…Although the oysters fed R. salina showed the best ingestion and absorption of the study, the values remained lower than those previously reported with C. gracilis and S. marinoï (≈ 5 mg g −1 h −1 : González-Araya et al, 2010). Absorption efficiency (ae%) ranged from 33 to 51%, while those obtained with the four other microalgae tested in our sister study ranged from 19 to 46% (González-Araya et al, 2010). It is interesting to note that, whichever of the eight different species the microalgae was supplied, O. edulis absorption efficiency on single diets was lower than that achieved with a mixed diet, as reported by Savina and Pouvreau (2004) who observed 80-90% ae with Glycymeris glycymeris and Phaphia romboïdes.…”

“…The techniques used in this study were previously detailed in González-Araya et al (2010), so only a brief outline will be given here.…”

“…As already pointed out, conditioning is an important step in hatchery production of molluscs and particular attention needs to be paid to flat oyster feeding during this stage because hatchery-conditioned broodstock has been found to have lower fecundity than wild stock (Helm et al, 1991). We had already made an initial study to look for an ideal diet for O. edulis (González-Araya et al, 2010). This work compared four monospecific microalgal diets based on ecophysiological and biochemical approaches, and assumed that the best microalgae should be those that were highly ingested, digested, assimilated and efficiently allocated to the reproductive compartment.…”